SPICAM-light on Mars-Express as a monitor of surface UV radiation and atmospheric oxidants

Abstract

The SPICAM-light optical package on the ESA Mars-Express mission includes a UV radiation channel to perform nadir and limb observation between 118 and 320 nm as well as an infrared channel extending between 1 and 1.7 μm. The UV resolution will be 0.5 nm per pixel. This spectral range was chosen for the observation of the total column and vertical distribution of ozone, aerosols and other gases; it is also aimed at the Martian upper atmosphere where the obtained data will help to constrain the escape problem. The associated infrared channel specialises in water vapour. The UV range corresponds exactly to the UV-B and UV-C spectral domains and will be used to determine the solar mid-UV radiation received at the surface and to establish its climatology. Signal simulations are performed using the results of a 2-D Martian model as input (Moreau, Thesis, Université Libre de Bruxelles, Brussels, Belgium 1995; Moreau, Fonteyn, Two-dimensional study of the atmospheric and surface oxidants on Mars, Proceedings of the Fifth International Conference on Mars, Lunar and Planetary Institute Contribution, Vol. 972, 1999, p. 6093) in order to show the influence of ozone and aerosol distributions on this radiation. Possibility of a UV shield exists during extreme polar ozone maxima as well as during dust storms, due to the UV absorption of Martian dust. In the other more normal cases, the daytime mid-UV radiation between 200 and 320 nm penetrates in sufficient amount to prevent the development of surface micro-organisms. Other life science conclusions could be drawn from the SPICAM-light observations: the direct mapping of water vapour will constrain the possible occurrences of subsurface liquid water that could be a favourable environment for the survival of life. SPICAM-light by its mapping of ozone and water vapour will also allow determining the amount of oxidants and especially OH. These could also affect the survival of Martian or contaminating bacteria. It is also intended to achieve a sufficient signal quality to measure an upper limit of lower atmospheric H2O2 and NO which are also related in diverse ways to living processes.© 2001 Elsevier Science Ltd. All rights reserved.